Distance measuring device and method of measuring distance by using the same

ABSTRACT

Provided is a distance measuring device and a method of measuring a distance. The distance measuring device detects light reflected by an object, generates an electrical signal based on the detected light, detects whether the electrical signal is saturated or not by comparing the electrical signal with a reference value, controls a magnitude of the electrical signal based on whether the signal is saturated, and calculates a distance to the object using the electrical signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/821,071, filed Nov. 22, 2017, which claims priority from KoreanPatent Application No. 10-2017-0085926, filed on Jul. 6, 2017, in theKorean Intellectual Property Office, the disclosures of which areincorporated herein in their entireties by reference.

BACKGROUND 1. Field

Apparatuses and methods consistent with exemplary embodiments relate todistance measuring devices for measuring a distance, and methods ofmeasuring a distance by using the same.

2. Description of the Related Art

Recently, 3D cameras and light detection and ranging (LIDAR) techniqueshave been studied for measuring a distance to an object. One distancemeasuring method is a time of flight (TOF) method that measures the timerequired for light to travel between an object and a camera. Thus, theTOF method is used for measuring a distance between an image capturingdevice and an object, creating a depth image.

The TOF method includes processes of irradiating light of a specificwavelength, for example, a near-infrared ray (850 nm), onto an object,by using a light-emitting diode (LED) or a laser diode (LD); measuringor capturing an image of the light of the specific wavelength asreflected by the object by using a photodiode or a camera; andextracting a depth image from the measured or captured image. VariousTOF methods have been developed utilizing optical processing, that is, aseries of processes including light irradiation, reflection by theobject, optical modulation, image capture, and processing. Discussionson methods of accurately measuring a distance to an object are ongoing.

SUMMARY

One or more exemplary embodiments may provide distance measuring devicesconfigured to correctly measure a distance by using light, and methodsof measuring the distance by using the distance measuring device.

Additional exemplary aspects will be set forth in part in thedescription which follows and, in part, will be apparent from thedescription, or may be learned by practice of the presented exemplaryembodiments.

According to an aspect of an exemplary embodiment, a distance measuringdevice includes: a light-receiver configured to detect light reflectedby an object and output an electrical signal based on the detectedlight; a peak detector configured to detect a peak from the electricalsignal; a saturation detector configured to detect whether theelectrical signal is saturated or not by comparing the electrical signalwith a reference value and to output a saturation detection result; anda processor configured to measure a distance to the object by using thepeak and to control a magnitude of the electrical signal by using atleast one of a peak detection result, the saturation detection result,and a measured distance to the object.

The processor may decrease the magnitude of the electrical signal whenthe magnitude of the electrical signal is greater than a referencevalue.

The light receiver may include a light detector that detects light whilea bias voltage is applied to the light detector.

The processor may control the magnitude of the electrical signal bycontrolling the bias voltage.

The magnitude of the electrical signal may be proportional to themagnitude of the bias voltage.

The light detector may include an avalanche photodiode (APD) or asingle-photon avalanche diode (SPAD).

The light receiver may further include an amplifier that amplifies anamplitude of the electrical signal.

The processor may control the magnitude of the electrical signal bycontrolling a gain of the amplifier.

The distance measuring device may further include a light sourceconfigured to irradiate light onto the object.

The processor may control the electrical signal by controlling a drivingsignal of the light source.

The magnitude of the electrical signal may be proportional to amagnitude of the driving signal.

The processor may increase the magnitude of the electrical signal whenthe peak is not detected by the peak detector for a certain period oftime.

The certain period of time may be greater than an emission frequency oflight of the light source.

The peak detector may detect the peak by using a constant fractiondiscriminator (CFD) method.

The processor may control the magnitude of the electrical signal inproportion to a calculated distance.

According to an aspect of an another exemplary embodiment, a method ofcalculating a distance, the method includes: detecting light reflectedby an object and outputting an electrical signal based on the detectedlight; detecting whether the electrical signal is saturated or not bycomparing the electrical signal with a reference value and outputting asaturation detection result; controlling a magnitude of the electricalsignal by using the saturation detection result; and calculating adistance to the object using the electrical signal.

The controlling of the electrical signal may include decreasing theelectrical signal when the magnitude of the electrical signal is greaterthan the reference value.

The calculating of the distance may include calculating the distance tothe object by detecting a peak from the electrical signal and increasingthe magnitude of the electrical signal when the peak is not detected fora certain period of time.

The magnitude of the electrical signal may be controlled by controllinga magnitude of a bias voltage applied to a light detector that detectsthe light.

The magnitude of the electrical signal may be controlled by controllinga magnitude of a driving signal of a light source that emits light.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other exemplary aspects and advantages will become apparentand more readily appreciated from the following description of exemplaryembodiments, taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a block diagram of a distance measuring device according to anexemplary embodiment;

FIG. 2A is a graph showing an example of an unsaturated signal;

FIG. 2B is a graph showing an example of a saturated signal;

FIG. 3 is a graph showing an example of magnitude of a bias voltageapplied to an object according to distances to the object;

FIGS. 4 and 5 are each a flowchart of a method of operating a distancemeasuring device 100, according to exemplary embodiments;

FIGS. 6A, 6B, 6C, 6D, and 6E are diagrams for explaining a wavelength ofa signal of a distance measuring device, according to an exemplaryembodiment;

FIGS. 7A, 7B, 7C, 7D, and 7E are diagrams of a waveform of a signal thatcontrols a driving signal of a light source according to saturationdetection, according to an exemplary embodiment; and

FIGS. 8A, 8B, 8C, 8D, 9A, 9B, 9C, and 9D are diagrams showing results ofsimulations of peak detections according to bias voltages.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. In the drawings, widthsand thicknesses of layers or regions may be exaggerated or reduced forclarity and convenience of explanation. Like reference numerals refer tolike elements throughout.

FIG. 1 is a block diagram of a distance measuring device 100 accordingto an exemplary embodiment. Referring to FIG. 1, the distance measuringdevice 100 may include a light source 110 configured to emit lighttoward an object 10, a light receiver 120 configured to detect the lightreflected by the object 10 and convert the reflected light into anelectrical signal, a peak detector 130 configured to detect a peak fromthe electrical signal, a saturation detector 140 configured to detect asaturation of the electrical signal by comparing the electrical signalwith a reference value, and a processor 150 configured to calculate adistance to the object 10 by using the peak.

The light source 110 may be a light-emitting device. For example, thelight source 110 may emit light having an infrared wavelength(hereinafter, infrared light). When a light source emitting infraredlight is used, light from the light source may be distinguishable fromnatural, visible light such as sunlight. However, the light emitted fromthe light source 110 is not limited to emitting infrared light, and mayalternately or additionally emit light in having any of variouswavelengths. In this case, a correction may be used for removinginformation of mixed natural light. For example, the light source 110may be a laser light source, but is not limited thereto. The lightsource 110 may be one of an edge emitting laser, a vertical-cavitysurface emitting laser (VCSEL), and a distributed feedback laser. Forexample, the light source 110 may be a laser diode.

The light receiver 120 may convert light reflected or scattered by theobject 10 to an electric signal, for example, a voltage. The lightreceiver 120 may include a light detector 122 configured to output anelectrical signal, for example, a current corresponding to light, acurrent-voltage conversion circuit 124 that converts a current outputtedfrom the light detector 122 into a voltage, and an amplifier 126 thatamplifies the amplitude of the voltage. In addition to the above, thelight receiver 120 may further include a lens that focuses lightreflected by the object 10 and a filter, for example, a high-pass filterthat filters an electrical signal of a specific frequency. The amplifier126 may amplify the amplitude of the voltage, but the amplifier 126 isnot limited thereto. The amplifier 126 may amplify the amplitude of thecurrent when disposed between the light detector 122 and thecurrent-voltage transformation circuit 124, or may be implemented as asingle circuit together with the current-voltage transformation circuit124.

The light detector 122 may be a light-receiving diode and may beoperated in a state in which a bias voltage Vbias is applied thereto.For example, the light detector 122 may include an avalanche photo diode(APD) or a single photon avalanche diode (SPAD). The light detector 122may be configured by a practical circuit in another way, for example,the light detector 122 may include an analog front end (AFE) or a timedigital counter (TDC) depending on which one of the APD and the SPAD isincluded as a light-receiving diode in the light detector 122. Theconfiguration of the practical circuitry of the light detector 122 maybe a well-known technique in the art, and thus, a detailed descriptionthereof is omitted.

The peak detector 130 may detect a peak from an electrical signalreceived from the light receiver 120. The peak detector 130 may detect apeak by detecting a central position of the electrical signal. Also, thepeak detector 130 may detect a peak by analogically detecting a width ofthe electrical signal. The peak detector 130 may detect a peak bydetecting a rising edge and a falling edge of a digital signal afterconverting the electrical signal to the digital signal. Also, afterdividing an electrical signal into a plurality of signals and invertingand time-delaying some of the divided signals, the peak detector 130 maydetect a peak by using a constant fraction discriminator (CFD) method inwhich a zero-crossing point is detected by combining the inverted andtime-delayed signals and the remaining signals. A circuit that detects apeak by using the CFD may be referred to as a CFD circuit. The peakdetector 130 may further include a comparator, and thus, may output thedetected peak as a pulse signal.

The processor 150 may calculate a distance to the object 10 by using apeak detected by the peak detector 130. For example, the processor 150may calculate a distance to the object 10 by using a time of the peakdetected by the peak detector 130 and a time of light emitted from thelight source 110. A method of measuring a distance by using a peak is awell-known technique in the art, and thus, a detailed description isomitted.

However, when light is irradiated onto a subject having a highrefractive index or a subject located near the distance measuring device100, the magnitude of the reflected light may exceed the dynamic rangeof the light receiver 120. Therefore, the light receiver 120 may outputan electrical signal of a certain magnitude, that is, a saturatedsignal. FIG. 2A is a graph showing an example of an unsaturated signal.FIG. 2B is a graph showing an example of a saturated signal. As isevident, it is more difficult to obtain a peak from a saturated signal.When the light receiver 120 outputs a saturated signal, a certain amountof time is required to restore the original, unsaturated state of thesignal, and thus, the light receiver 120 may output a signal having acharacteristic different from that of the actual signal. Also, if thelight receiver 120 outputs a saturated signal in some cases and outputsan unsaturated signal in other cases, an error may occur in detection ofthe peak.

The distance measuring device 100 according to the current embodimentmay further include the saturation detector 140 that detects whether anelectrical signal output from the light receiver 120 is saturated or notby comparing the electrical signal with a reference signal.

The saturation detector 140 may output an indication of a saturatedsignal, for example, “1”, when an electrical signal is greater than areference signal, and may output an indication of an unsaturated signal,for example, “0”, when the electrical signal is smaller than thereference signal.

The processor 150 may control the magnitude of an electrical signal byusing the indication output from the saturation detector 140. Forexample, the processor 150 may control the magnitude of an electricalsignal by controlling the magnitude of a bias voltage Vbias applied tothe light receiver 120, for example, to the light detector 122 of thelight receiver 120. Also, the processor 150 may control the magnitude ofan electrical signal by controlling the magnitude of a driving signal,for example, a driving current Id applied to the light source 110.

The bias voltage Vbias may be a potential difference applied to a powersupply (not shown) as the light detector 122 is operated, and themagnitude of an electrical signal output from the light detector 122 maydepend on the magnitude of detected light and may also depend on themagnitude of the bias voltage Vbias.

The magnitude of the bias voltage Vbias may depend on the location ofthe object 10, the optical sensitivity of the light detector 122, andthe power of the distance measuring device 100. FIG. 3 is a graphshowing an example of a magnitude of the bias voltage Vbias applied tothe light detector 122 according to the distance to the object 10. Asdepicted in FIG. 3, the processor 150 may change the magnitude of the abias voltage Vbias being applied to the light detector 122 according tothe distance to the object 10. For example, when the object 10 islocated within a distance of about 20 meters, the processor 150 maycorrectly measure the distance by applying a bias voltage Vbias with amagnitude in proportion to the distance to the object 10. Also, when theobject 10 is located at a distance of greater than 20 meters, theprocessor 150 may apply a maximum bias voltage Vbias, for example, 100V, to the light detector 122. The bias voltage Vbias may be changedaccording to the distance to the object 10, as described above, becausethe electrical signal output from the light detector 122 depends on themagnitude of the bias voltage Vbias. That is, when the magnitude of thebias voltage Vbias is small, the magnitude of the electrical signaloutput from the light detector 122 is small, and when the magnitude ofthe bias voltage Vbias is large, the magnitude of the electrical signaloutput from the light detector 122 is large. That is, the bias voltageVbias controls the gain of the light detector 122.

When the object 10 is located near the light detector 122 or the object10 has a large refractive index, the light receiver 120 may output anelectrical signal that exceeds a dynamic range, that is, the lightreceiver 120 may output a saturated signal, and the saturation detector140 may detect the saturation of the electrical signal by comparing theelectrical signal with a reference value. For example, when thesaturation detector 140 detects a saturated signal, the saturationdetector 140 may output a high-level pulse signal. Then, the processor150 may control the magnitude of the bias voltage Vbias to be small.Thus, the light receiver 120 may output a signal having a smallmagnitude, that is, an unsaturated signal. For example, the processor150 may control the magnitude of the bias voltage Vbias to be smallerthan 70% of the magnitude before being controlled.

Also, the processor 150 may control the magnitude of the electricalsignal by controlling the magnitude of a driving signal, for example, adriving current Id of the light source 110. The magnitude of lightreflected by the object 10 may be proportional to a refractive index ofthe object 10 and also proportional to the magnitude of light emittedfrom the light source 110. An electrical signal output from the lightdetector 122 may be proportional to the magnitude of light received bythe light detector 122. Thus, the magnitude of an electrical signaloutput from the light detector 122 may be proportional to the magnitudeof the driving signal of the light source 110. When the processor 150receives a saturation signal from the saturation detector 140, theprocessor 150 may control the magnitude of the driving signal of thelight source 110 to be small. Then, light having a small magnitude maybe irradiated onto the object 10, and accordingly, the magnitude ofreflected light may also be small. Therefore, the magnitude of theelectrical signal output from the light detector 122 becomes small, andthus, the light receiver 120 may output an unsaturated electricalsignal. For example, the processor 150 may reduce the magnitude of thedriving signal to be smaller than 70% of the magnitude before beingcontrolled.

Also, the processor 150 may control the magnitude of the electricalsignal by controlling a gain of the amplifier 126. The magnitude of anelectrical signal output from the light receiver 120 may be proportionalto a gain of the amplifier 126. Accordingly, when the processor 150receives a saturation signal from the light receiver 120, the processor150 may control the magnitude of the gain with respect to the amplifier126 to be small.

When the processor 150 receives an unsaturated signal, for example, alow-level signal from the saturation detector 140, the processor 150 mayomit additional control of the magnitude of the electrical signal.However, the current exemplary embodiment is not limited thereto. Theprocessor 150 may also appropriately control the magnitude of theelectrical signal according to a measured distance. That is, althoughthe processor 150 receives an unsaturated signal from the saturationdetector 140, the processor 150 may control the magnitude of theelectrical signal in proportion to the measured distance. For example,if the measured distance is smaller than a previously measured distance,the processor 150 may control the magnitude of the electrical signal tobe small, and if the measured distance is larger than the previouslymeasured distance, the processor 150 may control the magnitude of theelectrical signal to be large. A control range of the magnitude of anelectrical signal described above may be based on a look-up table thatshows a relationship between distance and the magnitude of theelectrical signal. The peak detector 130 may not detect a peak from anelectrical signal for a certain period of time. Here, the certain periodof time may be greater than a frequency of light emission from the lightsource 110. For example, the certain period of time may be about two tothree times greater than the frequency of light emission from the lightsource 110. If the magnitude of an electrical signal output from thelight receiver 120 is too small, the peak detector 130 may detect apeak. Then, the processor 150 may control the magnitude of an electricalsignal to be large. The processor 150 may control the magnitude of theelectrical signal by controlling the magnitude of the bias voltage Vbiasapplied to the light receiver 120, for example, the light detector 122,to be large. For example, the processor 150 may control the magnitude ofthe bias voltage Vbias to be 130% of the magnitude before controlling.When the magnitude of a bias voltage Vbias is large, the magnitude of anelectrical signal output from the light receiver 120 may also be large.

Also, the processor 150 may control the magnitude of the electricalsignal by controlling the magnitude of a driving signal, for example,the driving current Id of the light source 110. For example, theprocessor 150 may control the magnitude of the driving signal to begreater than 130% of the magnitude of the driving signal applied to theprocessor 150. If the driving signal is large, the magnitude of lightemitted from the light source 110 is large, and the magnitude of lightreflected by the object 10 becomes large. Also, the light receiver 120may output an electrical signal having a large magnitude, and the peakdetector 130 may detect a peak from the received electrical signal.

Also, the processor 150 may control the magnitude of the electricalsignal to be large by controlling the magnitude of a gain of theamplifier 126 to be large.

FIGS. 4 and 5 are each a flowchart of a method of operating a distancemeasuring device 100, according to an exemplary embodiment. FIGS. 6A,6B, 6C, 6D, and 6E are diagrams for explaining a wavelength of a signalof a distance measuring device 100, according to an exemplary embodimentof the inventive concept.

Referring to FIG. 4, the light receiver 120 receives light reflected bythe object 10. The light source 110 may emit light with a certain timeinterval to the object 10 (S410). As depicted in FIG. 6A, the lightsource 110 may emit light, for example, a laser pulse 610, at a certaintime interval. The light emitted from the light source 110 is reflectedby the object 10, and a portion of the reflected light may be receivedby the light receiver 120. The light source 110 may be one of an edgeemitting laser, a VCSEL, and a distributed feedback laser. For example,the light source 110 may be a laser diode.

The light receiver 120 may convert light reflected or scattered by theobject 10 into an electrical signal, for example, a voltage, and mayoutput the electrical signal (S420). Light reflected by the object 10may be focused on a lens, and the light detector 122 may output acurrent corresponding to the focused light. Also, the current-voltagetransformation circuit 124 may output a voltage by converting thecurrent to the voltage. The light receiver 120 may output an electricalsignal 620 as depicted in FIG. 6B. The light detector 122 may be alight-receiving diode, and may be operated in a state in which a biasvoltage Vbias is applied thereto. For example, the light detector 122may include an APD or a SPAD.

The saturation detector 140 may detect whether an electrical signaloutput by the light receiver 120 is saturated or not (S430). A portionof the electrical signal output by the light receiver 120 is applied tothe saturation detector 140, and a remaining portion of the electricalsignal may be applied to the peak detector 130. The saturation detector140 may output a pulse wave as an indication of whether the electricalsignal is saturated or not, by comparing the electrical signal with areference value. Vt depicted in FIG. 6B may be a reference value. Whenan electrical signal 620 a greater than the reference value is detected,the saturation detector 140 may, as depicted FIG. 6C, output a saturatedsignal 630, for example, a high-level pulse signal 630.

When the electrical signal is determined to be saturated (S430-Y), theprocessor 150 may control the magnitude of an electrical signal to besmall (S440). The processor 150 may control the magnitude of anelectrical signal by controlling the magnitude of exemplary bias voltageapplied to the light receiver 120, for example, the light detector 122,of the graph of FIG. 6D shows a waveform of a bias voltage. When asaturated signal 630 is detected, the processor 150 may control themagnitude of the bias voltage to be small, but the processor 150 is notlimited thereto. The processor 150 may also control the driving signalof the light source 110 to be small.

When the electrical signal is determined to be unsaturated (S430-N), theprocessor 150 may maintain the magnitude of the electrical signal(S450), but the processor 150 is not limited thereto. The processor 150may also appropriately control the magnitude of the electrical signalaccording to a measured distance to the object 10.

Referring to FIG. 5, the peak detector 130 may detect a peak from anelectrical signal output from the light receiver 120 (S510). The peakdetector 130 may detect a peak by detecting the central position of anelectrical signal. Also, the peak detector 130 may analogically detect apeak by detecting a width of an electrical signal. Also, the peakdetector 130 may detect a peak by detecting a rising edge or a fallingedge of a digital signal after converting an electrical signal to thedigital signal. The peak detector 130 may detect a peak by using a CFDmethod, and may output the detected peak as a digital signal by using acomparator, of the graph of FIG. 6E shows a waveform of a signal outputfrom the peak detector 130. When a peak is detected, as a result, thepeak detector 130 may output, for example, a high-level pulse 650.

When a peak is detected (S510-Y), the processor 150 may measure adistance to the object 10 by using a peak detection time (S520). Forexample, the processor 150 may measure a distance to the object 10 byusing a time difference between a peak detection time and a lightemission time. The method of measurement by using a peak is well knownin the art, and thus, a detailed description thereof is omitted.

When a peak is not detected (S510-N), the processor 150 may control themagnitude of an electrical signal (S530). When a peak is not detectedfor a certain period of time, the processor 150 may determine that themagnitude of an electrical signal is small, and thus, may control themagnitude of an electrical signal to be large. Here, the certain periodof time may be greater than a frequency of light emitted from the lightsource 110, for example, may be about two to three times greater than adriving frequency of light.

If a peak is not detected in a state in which the location etc. of theobject 10 is not changed, this may be the reason that the magnitude ofthe bias voltage Vbias is too small. Accordingly, the processor 150 maycontrol the magnitude of the electrical signal by controlling themagnitude of the bias voltage Vbias to be large. If a peak 650 a is notdetected in FIG. 6E, the processor 150 may control a magnitude 640 b ofthe bias voltage Vbias to be large, as shown by the signal waveform ofFIG. 6D, but the processor 150 is not limited thereto. The processor 150may control the driving signal of the light source 110 to be large.

FIGS. 7A, 7B, 7C, 7D, and 7E are diagrams of a waveform of a signal thatcontrols a driving signal of the light source 110 according tosaturation detection, according to an exemplary embodiment.

When the saturation detector 140 detects a saturated signal 730 adepicted in FIG. 7C, the processor 150 may, as depicted in FIG. 7A,control a magnitude 710 a of the driving signal of the light source 110to be small. Thus, as depicted in FIG. 7B, the magnitude of lightemitted from the light source 110 becomes small. Thus, the lightreceiver 120 may output an electrical signal 730 b having a smallmagnitude due to the light, the magnitude of which is reduced.Meanwhile, as depicted in FIG. 7E, if a peak 750 a is not detected bythe peak detector 130 for a certain period of time, the processor 150may re-control a magnitude 710 b of the driving signal of the lightsource 110 to be large. For example, the processor 150 may control themagnitude of the driving signal to be the original magnitude.

FIGS. 8A, 8B, 8C, 8D, 9A, 9B, 9C, and 9D are diagrams showing results ofsimulations of peak detections according to bias voltages. As depictedin FIG. 8A, in a state in which a bias voltage Vbias of −154 V isapplied to the light detector 122, the light detector 122 outputs asaturated signal 810 as depicted in FIG. 8B. A CFD circuit of the peakdetector 130 that receives the saturation signal outputs a signalwaveform as depicted in FIG. 8C, and a comparator of the peak detector130 outputs a signal waveform as depicted in FIG. 8D. The signalwaveform of FIG. 8D is output with two falling edges 820, and thus, anerror may occur in the processor's 150 determination of a peak time.

As depicted in FIG. 9A, a controlled bias voltage Vbias of −54 V isapplied to the light detector 122. The magnitude of the controlled biasvoltage Vbias is about 36% of the magnitude of a bias voltage Vbiasbefore being controlled. As depicted in FIG. 9B, an electrical signal910 output from the light receiver 120 is not saturated. A CFD circuitof the peak detector 130 outputs a signal waveform as depicted in FIG.9C, and a comparator of the peak detector 130 outputs a signal waveformas depicted in FIG. 9D. Since the signal waveform depicted in FIG. 9D isoutput with only one falling edge 920, the processor 150 may correctlydetermine the peak time.

As described above, since the magnitude of the electrical signal of thelight receiver 120 is controlled so that the light receiver 120 outputsan unsaturated signal, an error between a saturated signal and anunsaturated signal may be reduced.

As described above, in order to control the magnitude of an electricalsignal of the light receiver 120, the application of a bias voltage tothe light detector 122 or a driving signal of the light source 110 iscontrolled. However, the current exemplary embodiment is not limitedthereto. That is, in order to control the magnitude of the electricalsignal, the magnitude of a gain with respect to a constituent element,for example, the amplifier 126, may also be controlled.

While exemplary embodiments have been shown and described, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope as defined by the appended claims. The embodiments should beconsidered in descriptive sense only and not for purposes of limitation.Therefore, the scope is defined by the appended claims, and alldifferences within the scope will be construed as being included in theinventive concept.

What is claimed is:
 1. A distance measuring device comprising: a lightreceiver configured to detect light reflected by an object and to outputan electrical signal based on the detected light; a peak detectorconfigured to detect a peak from the electrical signal; a saturationdetector configured to compare the electrical signal with a referencevalue and thereby detect whether the electrical signal is saturated ornot saturated and output a saturation detection result; and a processorconfigured to measure a distance to the object by using the peak and tocontrol a magnitude of the electrical signal based on at least one ofthe detected peak, the saturation detection result, and a measureddistance to the object, wherein the light receiver further comprises anamplifier that amplifies an amplitude of the electrical signal and, inresponse to a first saturation detection result that the electricalsignal is saturated, the processor is further configured to reduce themagnitude of the electrical signal by controlling a gain of theamplifier.
 2. A distance measuring device of claim 1, wherein themagnitude of the electrical signal is proportional to the magnitude ofthe gain.
 3. The distance measuring device of claim 1, wherein theprocessor is further configured to increase the magnitude of theelectrical signal when no peak is detected by the peak detector for acertain period of time.
 4. The distance measuring device of claim 3,wherein the processor is configured to increase the magnitude of thegain when no peak is detected by the peak detector for the certainperiod of time.
 5. The distance measuring device of claim 3, wherein thecertain period of time is greater than a light emission period of alight source irradiating the object.
 6. The distance measuring device ofclaim 1, wherein, in response to a second saturation detection resultthat the electrical signal is not saturated, the processor is furtherconfigured to keep a magnitude of the gain of the amplifier.
 7. Thedistance measuring device of claim 1, wherein, the saturation detectoroutputs the saturation detection result as a pulse signal.
 8. Thedistance measuring device of claim 1, wherein the peak detector detectsthe peak by using a constant fraction discriminator (CFD) method.
 9. Thedistance measuring device of claim 1, wherein the processor is furtherconfigured to control the magnitude of the electrical signal inproportion to the measured distance to the object.
 10. A method ofcalculating a distance, the method comprising: detecting light reflectedby an object; outputting an electrical signal based on the detectedlight reflected; comparing the electrical signal with a reference value,detecting whether the electrical signal is saturated or not saturatedbased on the comparing, and outputting a saturation detection result;controlling a magnitude of the electrical signal based on the saturationdetection result; and calculating a distance to the object based on theelectrical signal, wherein the outputting the electrical signalcomprises amplifying an amplitude of the electrical signal by anamplifier, and the controlling the magnitude of the electrical signalcomprises reducing the magnitude of the electrical signal by controllinga gain of the amplifier.
 11. A distance measuring device comprising: alight source configured to irradiate light onto an object; a lightreceiver configured to detect light reflected by the object and tooutput an electrical signal based on the detected light; a peak detectorconfigured to detect a peak from the electrical signal; a saturationdetector configured to compare the electrical signal with a referencevalue and thereby detect whether the electrical signal is saturated ornot saturated and output a saturation detection result; and a processorconfigured to measure a distance to the object by using the peak and tocontrol a magnitude of the electrical signal based on at least one ofthe detected peak, the saturation detection result, and a measureddistance to the object, wherein, in response to a first saturationdetection result that the electrical signal is saturated, the processoris configured to reduce the magnitude of the electrical signal bycontrolling a driving signal of the light source.
 12. A distancemeasuring device of claim 11, wherein the magnitude of the electricalsignal is proportional to the magnitude of the driving signal.
 13. Thedistance measuring device of claim 11, wherein the processor is furtherconfigured to increase the magnitude of the electrical signal when nopeak is detected by the peak detector for a certain period of time. 14.The distance measuring device of claim 13, wherein the processor isconfigured to increase the magnitude of the driving signal when no peakis detected by the peak detector for the certain period of time.
 15. Thedistance measuring device of claim 13, wherein the certain period oftime is greater than a light emission period of the light source. 16.The distance measuring device of claim 11, wherein, in response to asecond saturation detection result that the electrical signal is notsaturated, the processor is further configured to keep a magnitude ofthe driving signal of the light source.
 17. The distance measuringdevice of claim 11, wherein, the saturation detector outputs thesaturation detection result as a pulse signal.
 18. The distancemeasuring device of claim 1, wherein the peak detector detects the peakby using a constant fraction discriminator (CFD) method.
 19. Thedistance measuring device of claim 11, wherein the processor is furtherconfigured to control the magnitude of the electrical signal inproportion to the measured distance to the object.
 20. A method ofcalculating a distance, the method comprising: irradiating light onto anobject by a driving signal of a light source; detecting light reflectedby the object; outputting an electrical signal based on the detectedlight reflected; comparing the electrical signal with a reference value,detecting whether the electrical signal is saturated or not saturatedbased on the comparing, and outputting a saturation detection result;controlling a magnitude of the electrical signal based on the saturationdetection result; and calculating a distance to the object based on theelectrical signal, wherein, in response to a saturation result that theelectrical signal is saturated, the controlling the magnitude of theelectrical signal comprises reducing the magnitude of the electricalsignal by controlling the driving signal of the light source.